Bi-lams, not lugs

Lugged frames are as popular now as in the 1940s. In the early years of cycling using lugs was the easiest way to make a frame. A lug is a socket that forms the junction between two or more frame tubes. Frame builders would use lug design as a method of differentiating their frames. Lugs are still used today both in carbon, aluminium and steel frame production. The Paris frames were innovative; the head tube design was created using a bi-lamination rather than a hand cut lug.

A bi-lamination requires more precision in the manufacturing process. Firstly on a flat sheet of steel a design is cut. It is then manipulated by hand to join both ends together so that it resembles a lug. Paris bi-lams are then slotted onto the head tube.

Next comes the tricky part. The tubes meeting the bi-lam must perfectly meet the back of the bi-lam and sit flush. Tubing must be cut and mitred exactly to the curve of the head tube.If it doesn't, either the bi-lam or the tube must be reworked or thrown away and the process begins again.

The tube must sit perfectly because any gaps will compromise the integrity of the join. Brass is then built up around the bi-lam and adjoining tube - a technique known as fillet brazing. The frame is then cooled and cleaned using water and a wire brush. Finally the brass is filed down by hand to achieve a smooth finish.

Why use bi-lams? The overall effect is a lighter frame and strong weld. Bi-lamination designs don't feature as much as lugs because of the man hours that goes into producing the frame. There is less room for error and error is costly to the frame builder. As fashion changed simple frame styles grew in popularity. Tig welding techniques meant a frame could be made quickly with the same strength but less weight compared with a lugged frame and, importantly, at a better price. Equipment for tig welding became precise and tig welding became an industry standard.